Constant potential system



Oct. 13, 1936. w. VAN B. ROBERTS CONSTANT POTENTIAL SYSTEM June 2Patented Oct. 13, 1936 l UNITED STATES CONSTANT POTENTIAL SYSTEM Waltervan B. Roberts, Princeton, N. J., assignor to Radio Corporation ofAmerica, a. corporation of Dealware Application June 2, 1932, Serial No.614,899

6 Claims.

`My present invention relates to constant potentialsystems, and moreparticularly to a high frequency transmission network utilizing a pairof electron discharge tubes arranged in a constant potential system.

On-e of the main objects of mypresent invention is to provide a highfrequency detecting or amplifying system wherein a pair of electrondischarge tubes are arranged to have their input 10 circuits in pushVpull relation, and their anode circuits in series with a source ofconstant potential. Y

; Another important object of the present invention is to provide a highfrequency amplifying arrangement which consists of a pair of electrondischarge tubes having their input circuits arranged to receive energyto be amplified in opposite phase, and anode circuits connected inseries with a source of constant potential, the control grids ofthetubes being unequally biased whereby upper and lower amplificationlimiting points are secured. ,j Another object of the present inventionis to provide a detector for use between a radio frequency amplifier anda low frequency amplifier,

the detector comprising a pair of electron discharge tubes vhaving theircontrol electrodes equallyv biased, and having their input circuitsarranged to receive energy from the preceding amplifier in oppositephase, theanode circuits of the detectortubes being arranged in serieswhereby the detector stage is capable of handling relatively high radiofrequency input voltage, and additionally results in a minimization ofthe fundamental radio frequency component of the energy detected. y

Still other objects of the present invention are to provide a highfrequency transmission network which'includes a pair of electrondischarge tubes 40 Whose input circuits are arranged to receive energyto be transmitted in opposite phase, and means for biasing the grids ofthe two tubes in predetermined manner so as to operate the network as adetector or an amplier, the anode circuits of the two tubes beingarranged in series relation. Y

And still further objects of the present invention arev to improvegenerally the simplicity and efficiency of high frequency transmissionnetworks, vand to particularly provide a network which is not onlyreliable in operation, but capable of utilization as a detector or anamplifier.

The novel features which I believe to be characteristic of my inventionare set forth in particularity in theappended claims, theinventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin connection with the drawing in which I have indicateddiagrammatically one circuit organiza- 5 tion whereby my invention maybe carried into effect.

In th-e drawing,

Fig. 1 diagrammatically shows a radio receiving system embodying thepresent invention, l0

Fig. 2 graphically illustrates the operation of the present invention.

Referring now to the accompanying drawing, and particularly Fig. 1,there is shown in the latter a network comprising electron discharge l5tubes I and 2. The input electrodes, the cathode and control grid, oftube I are coupled to a tunable oscillation circuit by means of aninductance coil 3, the grid circuit of tube I including an adjustablenegative bias source C'. 20 'Ihe input electrodes of tube 2 are coupledto the same tunable oscillation circuit including condenser 4 by meansof coil 6, it being noted that an adjustable grid biasing source C isconnected between the cathode and grid of tube 2.

The anode of tube I is connected to the positive terminal of a source Bof anode potential, the anode of tube 2 being connected to the cathodeof tube I, and the negative terminal of the source B being connected tothe cathode of 30 tube 2 through a resistor 8. The source of energy forthe tuned circuits of tubes I and 2 comprises a network 9 which may be amulti-stage radio frequency amplifier having a tunable input circuitincluding a variable condenser I0. Of course, the 35 radio frequencyamplifier 9 may comprise one or more stages of radio frequencyamplification, each of which stages has a tunable input circuit, andtherefore it should be clearly understood that the tunable input circuitincluding the va- 40 riable condenser I0 conventionally represents suchone or more tuned radio frequency input circuits. For simultaneous andsimilar tuning of the condensers I0 and 4, a mechanical unicontrol I I,shown in dotted lines, may be utilized. 45 A coil I2 is arranged tocouple the output of the amplifier 9 to the input circuit of tube I,while a coil I3 is arranged to couple the amplifier output to the inputcircuit of tube 2. It will be seen from the diagram that the energiessupplied to 50 tubes I and 2 are in phase opposition.

Any desired type of source of signal energy may be coupled, as at M, tothe tunable input circuit of the amplier 9. The source of signal energymay comprise the usual grounded antenna cir- 55 cuit, aV loop antenna,or even a radio frequency transmission line. The terminal of resistor 8which is connected to the negative side of source B is'coupledto thegrid of a succeeding electron discharge tube 20 through a couplingcondenser 2|, the cathode of tube 20 being connected to the oppositeside of resistor 8. The resistor 8 is Shunted by a'xed condenser 22;Acpotential source i3' is arranged in the output circuit of tube 20.inorder to provide proper Vpositive potential for the anodeof tube 2D, andbetween the grid. and cathode of tube 2li-is arranged a series pathVwhich includes a bias resistor 23 in series with a source of negativegrid bias potential 24. Any

well known type of utilization means may be coupled to the outputcircuit of tube 20, it being understood by those skilled in the art thatsuch,

a utilization means may comprise `a loud speaker,

headphones, or any other desired type of loud where Bzvoltage of batteryB, Cr=voltage of battery C andv `c=amplication constant of the tubes.Let it be assumedv that the signal impressed upon the input circuit of,tubes I and 2 is a 500 cycle tone, and e is adjusted to be at least asgreat as the cut-off value given above, then the current in will falltozero atk each half cycle of the tone., rising to the maximum value shownin Fig. 2 between each fall. This creates a 1,000 cycle tone in thereproducer coupled to the output of tube 20. Thus, in Fig. 2, point D`'shows the point which is used for detector operation, in this case thebias on the grids of tubes I and 2 being equal. That is cuzco. With thecircuitadjusted in this manner the.Y network including tubes I and 2operates as a power detector, and suppresses the fundamental radiofrequency component.

The Yvirtue of the VVarrangement is that when Y operatedat full output,no interfering signal or static crash, can cause any more variation incurrent through resistor'8-than the signal does. In order to make theresulting loudness or deafening effect in the reproduceras'small'as'possible, it is advisable to shunt theresistor 8 with aslarge a capacity as is possible without too greatly weakening thesignals.V Thiscapacity 22 prevents extremely sudden changes'of currentin the reproducer Veven if an extremely sudden voltage is applied to thetubes I and 2 along with the desired signal. An elaborate low pass lterwould be preferable to this condenser. Y

' Incase a signal is desired without the detecting and frequencydoubling effect discussed Vheretofore, unequal bias may be put on thetubes I and 2, so that Athe operating point lies on the straightest partlof the characteristic, and representedV in Fig. 2 by the symbolA.` Whenthe grid biases of tubes YI and 2 are adjusted in this manner, thenthe'network including tubes I and 2 operates Yas an amplifier; that isec is not equal to ec.V If the desired signal varies the current fromnearly zero coupled across said resistor.

to nearly maximum, the static to signal current ratio will not greatlyexceed unity. It will also be observed that Vwhen the tubes I and 2 arebiased to point A of Fig. 2, then there exists an' upper and lowerlimiting action on the output current.

Of course, when the network including tubes I and 2 operates as anamplifier of high frequency energy, then a succeeding tube such as 20must be adjusted to operate as a detector, and the detector tube wouldpreferably be followed by an audio frequency ampliner. It should also beobserved Vthat when the network including tubes I and 2 operates as apower detector, it is capable of handling input voltages up to largemagnitudes "such as for example 40 volts, and is capablerof deliveringan output of the same order of magnitude.

While I have indicated and described several systems for carrying myinvention into eifect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention 'as set forth inthe appendedclaims.V Y Y Y I What I claim is: Y

c 1. In combination in a high frequency transmission network, Aa Vpairof electron discharge tubes having their space discharge paths connectedin series and being provided with a common output circuit, a source ofconstant potentialk arranged in said common output circuit, theinputcircuits of said tubes being arranged to have energy to be transmitted,impressed upon them in opposite phase, and means'in each input circuitof each tubeV for negatively biasing the grid of each-tube in unequalmanner. n

2. In combination in a high frequency transmission network, a pair ofseries connected electron discharge tubes provided rwith acommon outputcircuit, a source of constant potential arranged in said common outputcircuit, the input circuits of said tubes Y being arranged to haveenergy to be transmitted, impressed upon them in opposite phase, meansfor unequally, and negatively, lbiasingthe grids-of said tubes, aresistor in said common output circuit, and an electron discharge tubehaving its input electrodes directly 3. A circuit for high leveldetection with suppression of radio frequency fundamental and exhibitingsharply defined saturation above a predetermined level, comprising `apair of series connected electron discharge tubes provided with a commonoutput circuit, a source of constant potential arranged in said vcommonoutput circuit, the input circuits of said tubes being arranged to haveenergy to be transmitted, impressed upon them in opposite phase, andmeans in each input circuit of each tube for, biasing the grid of eachtube in a predetermined manner with equal biases;

4. A circuit for linear amplication'with sharply defined saturationabove a predetermined level comprising Ya pair ofxseries connectedelectron discharge tubes provided with a common output circuit, a sourceof Yconstant potential arrangedV of large magnitudes, a power detectornetwork capable of delivering an output of the same order of magnitude,said network comprising a pair of tubes having the grids thereofconnected to the output circuit of said amplier, said connection beingsuch that the radio frequency voltages applied to the grids are in phaseopposition, means for normally maintaining said grids negatively biased,a source of constant potential in the anode circuit of one of the tubes,the anode to cathode path of the other tube being connected in serieswith said potential source and with the anode to cathode path of thesaid one tube.

6. In a radio receiver, a tunable, multi-stage radio frequency amplifieradapted to deliver radio 15 frequency voltages of large magnitudes ofthe order of 40 volts, a power detector network capable of delivering anoutput of the same order of magnitude, said network comprising a pair oftubes having the grids thereof connected to the output circuit of saidamplier, said connection being such that the radio frequency voltagesapplied to the grids are in phase opposition, means for normallymaintaining said grids negatively biased, a source of constant potentialin the anode circuit of one of the tubes, the anode to cathode path ofthe other tube being connected in series with said potential source andwith the anode to cathode path of said one tube.

WALTER VAN B. ROBERTS.

